Poly-4-hydroxybutyrate (P4HB, TephaFLEX® biomaterial) is a strong, pliable thermoplastic polyester that, despite its biosynthetic route, has a relatively simple structure
The polymer belongs to a larger class of materials called polyhydroxyalkanoates (PHAs) that are produced by numerous microorganisms (see, for example, Steinbüchel A., et al. Diversity of Bacterial Polyhydroxyalkanoic Acids, FEMS Microbial. Lett. 128:219-228 (1995)). In nature these polyesters are produced as storage granules inside cells, and serve to regulate energy metabolism, PHAs are also of commercial interest because of their thermoplastic properties, and relative ease of production. Several biosynthetic routes are currently known to produce P4HB. Poly-4-hydroxybutyrate (P4HB) and copolymers thereof can be produced using transgenic fermentation methods, see, for example, U.S. Pat. No. 6,548,569 to Williams et al., and are produced commercially, for example, by Tepha, Inc. (Lexington, Mass.). Chemical synthesis of P4HB has been attempted, but it has been impossible to produce the polymer with a sufficiently high molecular weight that is necessary for most applications (Hori, Y., et al., Polymer 36:4703-4705 (1995)). Copolymers of P4HB include 4-hydroxybutyrate copolymerized with 3-hydroxybutyrate or glycolic acid (U.S. patent application No. 20030211131 by Martin and Skraly, U.S. Pat. No. 6,316,262 to Huisman et al., and U.S. Pat. No. 6,323,010 to Skraly et al.). Methods to control molecular weight of PHA polymers are described in U.S. Pat. No. 5,811,272 to Snell et al.
U.S. Pat. No. 6,245,537 to Williams et al., U.S. Pat. No. 6,623,748 to Clokie, and U.S. Pat. No. 7,244,442 to Williams et al. describe methods of making PHAs with little to no endotoxin, which is suitable for medical applications. U.S. Pat. Nos. 6,548,569, 6,838,493, 6,867,247, 7,268,205, and 7,179,883 to Williams et al. describe use of PHAs to make medical devices. PHAs with controlled degradation and degradation in vivo of less than one year are described in U.S. Pat. Nos. 6,548,569, 6,610,764, 6,828,357, 6,867,248, and 6,878,758 to Williams et al. and WO 99/32536 to Martin et al. Applications of P4HB have been reviewed in Williams, S. F., et al., Polyesters, III, 4:91-127 (2002), and by Martin, D. et al. Medical Applications of Poly-4-hydroxybutyrate: A Strong Flexible Absorbable Biomaterial, Biochem. Eng. J. 16:97-105 (2003). Medical devices and applications of P4HB have also been disclosed by WO 00/56376 to Williams et al. Several patents including U.S. Pat. Nos. 6,555,123, 6,585,994, and 7,025,980 describe the use of PHAs in tissue repair and engineering. WO 04/101002 to Martin et al. discloses monofilament and multifilament knitted meshes of P4HB produced by knitting monofilament and multifilament fibers of P4HB.
In February 2007, Tepha obtained FDA approval to market P-4HB sutures, the first approval of a new medical polymer in decades. The TephaFLEX® Absorbable Suture has mechanical and biological properties that are uniquely applicable to implantable medical devices when compared to conventional synthetic and biologically derived polymers. Compared to synthetic polymers such as polylactic acid (PLA) and polyglycolic acid (PGA), TephaFLEX® material is tougher and more flexible with an absorption rate and degradation profile that are compatible with human tissue repair and replacement applications. However, unlike other biopolymers such as collagen and hyaluronate, TephaFLEX® polymer is a thermoplastic and can be fabricated into virtually any shape or form—including fibers, films, tubes, foams, textiles, microspheres, and molded constructs—using a wide range of conventional melt and solvent processing techniques.
In the practice of surgery, absorbable medical textiles are used in a number of applications including hernia repair, hemostasis, and soft tissue support. These products often consist of a woven or knitted design. Non-woven textiles, on the other hand, are made of a random collection of fibers. They are not typically used in these applications due to their lower strength and the loose nature of the fibers. Non-woven materials have been used, however, to create tissue engineering constructs. As such, there currently exists a need for absorbable non-wovens with improved performance. These non-wovens can be used, for example, to reinforce tissue structures, and to serve as tissue engineering scaffolds. They may also be used as components of other devices. A number of other absorbable materials have been used to produce non-wovens for medical application. For example, non-wovens have been made from polyglycolic acid (PGA) or copolymers containing lactic acid. These materials do not, however, have ideal properties for many surgical procedures and applications. Non-wovens made from polyglycolic acid break down too rapidly for many applications, and release acidic degradation productions that can cause inflammatory reactions. Additionally, non-wovens made from PGA, PLA and their copolymers have traditionally been made by cutting and carding felting techniques from staple fibers (i.e. short fibers) not from continuous fibers. The fibers in these types of non-wovens are held together by fiber entanglement and cohesion and thus the resulting felts have low cohesive strength, resulting in low burst strengths for the non-woven felts.
It is an object of the present invention to provide methods to produce non-wovens of absorbable polymers that have relatively high burst strengths and whose fibers are bonded together for improved cohesive strength.
It is a further object of the present invention to provide continuous processes to produce such non-wovens, such as melt blowing processes, as compared to melt extrusion of fibers followed by batch processes such as cutting, carding and needling (used to prepare staple non-wovens).
It is another object of the present invention to provide non-wovens which are biocompatible and can be used in medical applications, for example, as implants such as devices for temporary tissue support, devices or components of devices for tissue in-growth and tissue engineering, as wells as porous absorbable implants for delivery of therapeutic agents or materials.
It is yet another object of the invention to provide continuous processes for polymer non-woven production which yield materials with excellent physical and mechanical properties.